SQL 获取一些组并保持顺序

Question

我有一个示例数据如下。

+---------+------------+--------+
| user id |   sequence | Action |
|---------|------------|--------|
| 12345   |    1       | Run    |
| 12345   |    2       | Sit    |
| 12345   |    3       | Sit    |
| 12345   |    4       | Run    |
| 12345   |    5       | Run    |
| 12345   |    6       | Sit    |
+---------+------------+--------+

现在我希望结果应该是这样的：

+---------+---------+
| user id |  Action |
|---------|---------|
| 12345   |  Run    |
| 12345   |  Sit    |
| 12345   |  Run    |
| 12345   |  Sit    |
+---------+---------+

应合并序列#2 和#3 的行，#4 和#5 应合并。我使用 'group by Action' 会得到类似下面的答案 table，但这不是我想要的：

+---------+---------+
| user id |  Action |
|---------|---------|
| 12345   |  Run    |
| 12345   |  Sit    |
+---------+---------+

如何实现 SQL（我使用 Google Bigquery）？

万分感谢！

Answer 1

您可以使用 window 函数：想法是将每一行的操作与“上一个”操作进行比较，并过滤值发生变化的行：

select *
from (
    select t.*, lag(action) over(partition by user_id order by sequence) lag_action
    from mytable t
) t
where action <> lag_action or lag_action is null

Answer 2

下面是 BigQuery 标准 SQL

#standardSQL
SELECT * EXCEPT(dup) FROM (
  SELECT *, action = LAG(action, 1, '') OVER(PARTITION BY user_id ORDER BY sequence) AS dup
  FROM `project.dataset.table`
)
WHERE NOT dup

如果应用于您问题中的示例数据 - 输出为

Row user_id sequence    action   
1   12345   1           Run  
2   12345   2           Sit  
3   12345   4           Run  
4   12345   6           Sit

SQL 获取一些组并保持顺序

SQL to get some groups and keep the order

sql

select

window-functions

gaps-and-islands

google-bigquery